The present invention is directed to wire preforms for use in brazing.
The brazing process typically involves joining ferrous and non-ferrous metal components together by positioning a brazing composition (such as an aluminum or silver-bearing metal alloy) and a flux adjacent to or between surfaces of the components to be joined, also known as the faying surfaces. To form the joint, the metal alloy and flux and the faying surfaces are heated to a temperature typically above the melting temperature of the alloy but below the melting temperature of the components to be joined. The alloy then melts, flows into the faying surfaces by capillary action and forms a seal that bonds the faying surfaces to one another.
A flux composition is often applied to the faying surfaces prior to brazing. In one application, a flux can be selected so that, when applied, it does one or more of the following: (1) removes oxides ordinarily present on the faying surfaces; (2) promotes the flow of the molten brazing alloy when heated to a temperature above its melting point; and (3) inhibits further oxide formation on the faying surfaces.
Flux cored wire ring preforms for brazing are known to have been made using an aluminum/silicon metal alloy. When heated, the alloy tends to men quickly satisfactory joints to be made. A known supplier of flux cored aluminum rin preforms is Omni Technologies Corporation.
Initial attempts to make silver alloy flux cored braze ring preforms using the same design principles as the aluminum preforms met with little initial success, however. Specifically, when the silver preforms were heated, the flux would not disperse evenly about the rings but, rather, would exit only from opposite ends of the silver wire forming the preforms before melting of the wire itself. As a result the braze joint were poor.
Accordingly, there is a need for a flux cored braze ring preform that, during heating, will disperse its core flux material evenly about the ring and onto a surface to be treated for brazing. In particular, there is a need for such preforms made of silver alloys.
The present invention is directed to a flux cored brazing preform. A metal alloy is provided as an elongated thin sheet that is rolled around its long axis so as to encase a flux material. The rolled metal alloy sheet thus forms a flux cored wire having longitudinal seam through which the flux material, when in a molten state, can exit.
The flux cored wire is then shaped into a braze ring preform which when heated allows the encased flux material to flow uniformly from the seam about the circumference of the preform, and to disperse evenly for treating a surface to be